This invention relates to propeller drives or screw drives for watercraft, and is more specifically concerned with a device to protect the screw drive from fish line or other debris in the water, which may wind around the shaft and damage the drive mechanism. The invention more particularly addresses problems of work boats and vessels, such as trash skimmers, that operate in areas where there is considerable amounts of debris in the water.
A problem arises where there are strands of fish line in the water, as the fish line can catch on the screw or propeller, and then wind around the propeller shaft as the shaft rotates. The fish line can wind back towards the housing where the shaft emerges, and can damage the rubber seal that surrounds the propeller shaft at that location. This can result in leakage of lubricants out of the housing and of water into the housing.
There have been several proposed solutions for cutting debris away from a propeller shaft. One typical solution is described in U.S. Pat. No. 7,008,277. There, a spool is mounted on the propeller to provide a place for the debris to wind up, and a cutter in the form of a knife or blade is mounted on the skeg or body of the motor to cut away the debris that accumulates on the spool. This approach has not proved to be reliable, and in addition it presents an exposed sharp edge.